Electrical musical instrument of the type employing gaseous discharge tubes



W. E. KOCK ELECTRICAL MUSICAL INSTRUMENT OF THE TYPE EMPLOYING G'KSEOUSDISCHARGE TUBES Filed Dec. 11, 1935 J NE Q AT 0 u -w R Q Q 9 ma fuwbwhxN T z O M Q m N J 3 O-i hl l l l H .umS mt Patented Aug. 30, 1938ELECTRICAL MUSICAL INSTRUMENT OF THE TYPE EMPLOYING GASEOUS DIS- CHARGETUBES Winston E. Kock, Cincinnati, Ohio, assignor to The BaldwinCompany, Cincinnati, Ohio Application December 11, 1935, Serial No.53,955

8 Claims.

This invention relates to an electrical musical instrument of the typeemploying gaseous discharge tubes.

In instruments previously devised employing the ordinary glow tubeoscillators, difllculty has been experienced in obtaining suflicientstability of pitch, due to the fact that changes in the characteristicsof the glow lamps aifect the frequency of the electrical oscillationsgenerated.

Several methods overcome this to a certain extent] For example theinsertion of an inductance in the condenser circuit in order to obtainan inductive glow discharge oscillator, as described in my United StatesPatent No. 2,046,463, issued July 7, 1936, from an application SerialNo. 701,173, copending with this application, will materially reduce theinstability. However, this procedure requires an inductance for eachnote of the scale, which introduces weight and expense in an organ,where '73 to such oscillators may be required.

Another method is to provide coupling between those oscillators whichare at octave separation, since such oscillators have frequencies whichare harmonically related, and coupling means would cause them to lockinto step with one another.

For the ordinary glow discharge oscillator (the relaxation oscillator)this procedure is of no value because of the fact that in order toobtain sufliciently tight coupling to hold the various octaves in stepeven to within a semitone or so, a voltage from the other oscillatorsmust be used which would introduce objectionable harmonics andsubharmonics into the outputs of the individual generators. Couplingbetween oscillators of the inductive glow discharge type is moreeffective in this respect, due to the fact that their control circuits(inductance and capacity) resonate at the frequency of theircorresponding oscillators and the undesirable harmonic and subharmoniccomponents are automatically filtered out.

It is an object of this application to describe a novel coupling meanswhich dispenses with inductances for all but one octave, and completelyeliminates the undesirable presence of subor super-harmonics in theoutput of the generators.

In this method, use is made of the control action of the grid electrodeof a three-electrode discharge tube. If a three-electrode tube,operating as a relaxation oscillator, has a certain frequency ofoscillation with fixed grid bias, the introduction into the grid circuitof a small alternating.

voltage of a frequency 50% or even greater than this original frequencywill cause the discharge tube to oscillate at the frequency of thisimpressed grid voltage. Furthermore, frequencies at octave separationare easily obtained.

In the drawing Fig. 1 is a main oscillator and one an octave below.

Fig. 2 shows part of the circuit of an electrical musical instrument,including the circuit of Fig. 1.

Fig. 3 shows a filter circuit.

In Figure 1 oscillator 02 is oscillating at say 10 400 cycles, so that a400 cycle voltage appears across R2. With switch S1 open, oscillator 03is oscillating at say cycles. When switch S is closed and thealternating voltage on R2 is impressed on the grid of 03, the oscillator03 will lock into step at 200 cycles, so that 02 and 03 will be atoctave separation. This procedure can be cascaded to obtain oscillatorsoscillating at 100 cycles, 50 cycles, etc. so that the entire bank ofoscillators are at octave separation.

It is to be noted that a tendency for O3 to shift in pitch is nottransferred to 02. For example, a change in the condenser C2 will effectno change in the frequency of 03 until the natural frequency of 03 (i.e. the frequency at which it would oscillate with no A. C. voltage onits grid) exceeds the differential of 5 or 6 semitones in eitherdirection. This presents a marked distinction between the method ofthree-electrode and two-electrode tubes. In order to couple a plu ralityof two-electrode tubes, the voltage from each tube must be impressed onall of the remaining tubes, so that a tendency for any single oscillatorto shift in pitch will cause the rest of the coupled tubes to shift inpitch. Of course, this shift will be smaller with coupling than without,nevertheless there will be some shift. With threeelectrode tubes, on theother hand, each oscillator influences only the tube an octave below it,sothat if the top master oscillator is of constant frequency, all of theremaining tubes will exhibit constant frequency. In Fig. 1, for example,03 cannot affect the pitch of O2, and if the grid of a third oscillatorwere coupled to 0: it could not afiect the pitch of 0:. nor of O2, andso forth.

However, an even more important distinction is the absence of thecoupling voltage in the outputs of the various generators. For example,in Fig. 1, although 02 oscillates at 400 cycles and O; at 200, thevoltage output of 03 contains no' trace of the additional 400 cyclecoupling voltage. The is due to the unique characteristic of athree-electrode glow tube, the failure of the grid to aifect the platecurrent once the discharge has been initiated. In Fig. 1, because 03 hasa 400 cycle voltage on its grid, the grid will go slightly positivetwice in every cycle of the discharge current (200 cycles). on one ofthese twooccasions, it will trigger the discharge, whereas, on theother, it will have no influence on the plate current. Thus eachoscillator will generate a rich tone of the correct fundamentalfrequency and all will be dependent on the top master oscillator.

Fig. 2 shows an arrangement of three tubes, using as a top masteroscillator 01, the grid coupled inductive glow discharge oscillator asdescribed in my previous application, Serial 16,449, series of 1935,which, as was pointed out, possesses extreme stability. The lowergenerators, O2 and 0:, are simple relaxation oscillators and hencerequire no inductanoes. With 01 oscillating, a voltage of frequency 2093(corresponding to high C) is developed on resistor R1, and by means ofthe connection RC, this voltage is impressed on the grid of oscillator02. This causes oscillator 0: to pull into step at 1046.5 cycles(corresponding to the next octave below )and a voltage of that frequencyis developed across R2. This is then impressed on the grid of O: causingit to oscillate at 523.3 cycles and a voltage of that frequency isdeveloped on B1. The circuit diagram shows only three oscillators, butas many as desired could be used. For a complete organ there would be 6or '7 octaves, therefore each master oscillator would control 5 or 6other tubes, and since there are 12 notes in an octave, 12 masteroscillators would be required and 60 to 72 relaxation oscillators.

As indicated in Figure 2, the leads L1, La and L: can be connectedthrough decoupling resistors R5 to switches S, which in turn areconnected through resistors Re to transformers T1 and T2. In theapparatus labeled T. C. various tone colors and timbres can be impartedto the notes, which may then be amplified in A and transferred intosound by the loudspeaker L. S. The tone color device T. C. #1 is used toaccentuate the high harmonics to give string and reed quality to thenotes, and the device T. C. #2 is used to filter out the high harmonicsto give a pure, flute-toned quality. Without the resistances Re and withonly T. C. #2 in operation, the high frequency note on Ll would beattenuated more than the low frequency note on L: because the filterdevice T. C. #2 suppresses the high frequencies. In the same way,without Rs and with only T. C. #1 in operation, the high frequency noteon L1 would have a much greater intensity than the low note on LJ. Byproper selection of Re and the primary impedances of Ti and T2, thenotes all over the scale can be equalized in intensity, whether flutequality or rich quality is played. By making R5 large in comparison withR1, R2. R: and the primary impedances T1 and T2, the playing of severalnotes simultaneously will not affect the pitch or intensity of anysingle note.

Switch 81 permits the application of a pitch or frequency vibrato to theissuing notes. The generator G supplies an alternating voltage of 4 to 6cycles per second and thus periodically varies the grid bias of themaster oscillator. A sufllcient voltage swing can change the pitch ofthe master oscillator enough to produce a pleasing vibrato, and sincethe master oscillator has complete control over the frequencies of theremaining oscillators, a vibrato is produced on all notes.

1 1g. 3 shows a type of filter which is very eflective in producing aflute quality tone from an oscillation which is rich in harmonics. Thisfilter would correspond to T. C.'#2 in Fig. 2. The oscillations are fedin at I and taken out at 0. 'I'hecondensers C form low impedance pathsto the high frequency notes and the signal at 0 is very free fromharmonics. Such an arrangement would discriminate against those tones ofhigh fundamental frequency, but as explained before, an arrangement asshown in Fig. 2, where the resistors Rs cut down the intensities of thelow notes before they reach T. C. #2, produces final signals ofapproximately equal intensity throughout the scale. Although such afilter system is not novel, it is believed that this method has notheretofore been applied to electrical musical instruments. Most filtersin such instruments comprise inductances, which cause them todiscriminate against certain bands of frequencies.

The important improvements which I have herein set forth may thus besummarized:

First, a new method of controlling the frequency of severalthree-electrode glow tube oscillators in cascade, thereby preventing anyfluctuations in succeeding tubes from affecting the pre ceding tube ortubes, and thereby yielding no undesirable subor super-harmonics in theoutputs of the individual generators.

Second, the use of a grid coupled inductive glow discharge oscillator inan electrical musical instrument as the topmost or master oscillator, inconjunction with which the above mentioned control system produces avery rigid bank of 0scillators.

Third, a method whereby the intensities of notes of widely differenttone color are equalized throughout the scale.

Although the grid coupled inductive glow discharge oscillator has beendescribed in my previous application, Serial 16,449, series of 1935, itsuse in an electrical musical instrument as a stable oscillator is hereinset forth for the first time.

I claim:

1. In an electrical musical instrument, a plurality of electricaloscillation generators, each of said generators comprising a gaseousglow discharge tube of a type having an anode, a cathode and a grid, andmeans for applying a voltage generated by one of said oscillationgenerators to the grid of a second of said oscillation generators,whereby to cause said second oscillation generator to oscillate at afrequency bearing a definite and fixed relationship to the frequency ofthe first mentioned oscillation generator.

2. In an electrical musical instrument, a plurality of electricaloscillation generators, each comprising a gaseous glow discharge tubehaving an anode, a cathode and a grid, oscillation circuits for saidoscillation generators, and means for impressing a voltage generatedbyone of said oscillation generators upon the grid of a second of saidoscillation generators whereby to cause the last mentioned generator tooscillate at a frequency which is some harmonic fraction of thefrequency of the first mentioned oscillation generator.

3. In an electrical musical instrument at least three oscillationgenerators arranged in cascade, each of said generators comprising agaseous glow discharge tube having an anode, a cathode and a grid, saidoscillation generators having oscillation circuits, means for impressing3. voltage generated by the first of said oscillation generators uponthe grid of the second of said oscillation generators whereby to causesaid second amass? oscillation generator to oscillate at a frequencywhich is some harmonic fraction of the frequency of said firstoscillation generator,- and means for impressing upon the gridiof thethird of said oscillation generators a voltage generated by the secondof said oscillation generators whereby to cause, said third generator tooscillate at a frequency which is some harmonic fraction of'thefrequency of said second oscillation generator.

4. Inan electrical musical instrument, a master oscillator or source ofpulsating voltage, and a plurality of electrical oscillation generators,each comprising an oscillation circuit and a gaseous glow discharge tubehaving an anode, a cathode and a grid, means for impressing the voltageproduced by said master oscillator upon the grid of a second of saidoscillators to cause the second oscillator to oscillate at a frequencywhich is half the frequency of the master oscillator, means forimpressing a voltage generated by said second oscillator, upon the gridof a third oscillator whereby to cause'said third oscillator tooscillate at a frequency which is half the frequency of said secondoscillator and so on throughout the eascaded series.

5. The cascade of oscillation generators as claimed in claim 4, whereinsaid master oscillation generator comprises a gaseous glow dischargetube having a feed circuit and a control circuit, the frequency ofoscillation thereof being determined by both capacity and inductance insaid control circuit.

6. The cascade of oscillation generators as claimed in claim 4, in whichsaid master oscillator comprises a gaseous glow discharge tube having ananode, a cathode and a grid, a feed circuit therefor and a controlcircuit therefor containing an inductance and a capacity by the combinedeffect of which the frequency of said oscillator is stabilized, andmeans for energizing said grid with a pulsating frequency derived fromsaid control circuit.

7. In an electrical musical instrument, a plurality of masteroscillation generators arranged to oscillate at frequencies related toeach other as the notes of the scale, in a high register, and, for

each of said master oscillation generators a cascade of controlledgenerators, said last mentioned generators comprising each a gaseousglow discharge tube having an anode, a cathode and a grid, and asemi-tuned controlled circuit, means for impressing a voltage generatedby a master oscillator on the grid of an oscillator in its cascade,means for impressing a voltage generated by said last mentionedoscillator on a succeeding oscillator and so on throughout each cascadewhereby the generators in said cascades are caused to oscillate, each ata frequency which is half the frequency of the generator next highest inthe cascade.

8. In an electrical musical instrument, a plurality of masteroscillation generators arranged to oscillate at frequencies related toeach other as the notes of the scale, in a high register, and, for eachof saidmaster oscillation generators a cascade of controlled generators,said last mentioned generators comprising each a gaseous glow dischargetube having an anode, a cathode and a grid, and a semi-tuned controlledcircuit, means for impressing a voltage generated by a master oscillatoron the grid of an oscillator in its cascade, means for impressing avoltage generated by said last mentioned oscillator on a succeedingoscillator and so on throughout each cascade whereby the generators insaid cascades are caused to oscillate, each at a frequency which is halfthe frequency of the generator next highest in the cascade, and meansfor deriving from said oscillators portions of the voltage generatedtherein for amplification and reproduction.

WINSTON E. KOCK.

CERTIFICATE OF CORRECTION. Patent No. 2,128,367. August 50, 1938.

w WINSTON E. xocx.

It is hereby certified that error appears in the above numbered patentrequiring correction as follows: In the drawing, Figures 1 and 2 shouldappear as shown below instead 01 as in the present drawing of thepatentand that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 6th day of December, A. D. 1958.

Henry Van Arsdale

